the Royal Society’s Infiruments. 401 
within 1 4', which is a difference confiderabiy lels than I 
fhould have expected. It appears alfo, that the dipping- 
needle, in the lituation in which it is placed at the So- 
eiety’s Houfe, is not much affefted by any iron work, as 
the dip Ihewn by it in the garden differs only 7' from 
that fet down in the journal of the weather. 
According to norman, the inventor of the dipping- 
needle, the dip at London in the year 1 5 7 6 was 7 1 0 5 o f ( 0 ; 
in 1676 it was 73 0 47', according to Mr. bond.'/;; Mr. 
whiston in 1720 made it 75 0 ioV*;; Mr. graham in 
1723 made it between. 7 3-! or 7 5 0 w, his different trials 
varying fo much ; and at prefent it appears to be 7 2 0 30'. 
I do not know how much Mr. bond’s determination is to 
be depended on, as he does not fay by what means he 
arrived at it; but, I believe, Mr. whiston’s is pretty ac- 
curate, for he obferved the dip in many parts of the 
kingdom, and the obfervations agree well together ; fo 
that it is reafonable to fuppofe, that his inltrument was a 
good one, and that he obferved in places where the needle 
was not much influenced by iron w ork. The dip, there- 
fore, feems to have been confiderabiy greater about the 
year 1720, than it was in norman’s time, or is at pre- 
fent: it appears, however, to alter very flowly in com- 
parifon of the variation. 
( e ) New Attractive, c. 4. (f) Longitude found, p. 65. 
(g) Longitude and Latitude found by Dipping-needle } p. 7, 49, and 94. 
( b ) Phil. Tranf. N° 3S9. p. 332. 
XXII. An 
